The present invention is generally directed to processes for the preparation of conductive polymeric coatings and articles thereof, and more specifically to carrier and developer compositions treated with the conductive coatings, by for example, a dry powder process, for use in two component electrophotographic imaging processes. In embodiments of the present invention, carrier particles are comprised of a core with a conductive coating thereover generated from colloidal powders comprised of intrinsically conducting polymers which reside in the interstices of the amorphous regions of fluorinated polymers. The conductive colloidal powders are prepared by solubilizing concentrated ionic solutions, of for example, about 10 to about 75 percent by weight of a redox salt, in the amorphous regions of commercially available fluorinated polymers and related resins, such as polyvinylidene difluoride (PVF.sub.2). Subsequent exposure of the solubilized redox salt and fluoropolymer mixture to the vapor of a redox polymerizable monomer or a solution of a redox polymerizable monomer in a non solvent for PVF.sub.2 and the ionic redox salt, results in the rapid formation of intrinsically conducting polymers (ICPs) interstitially in the amorphous regions of the PVF.sub.2 powder. An essential particulate characteristic of the PVF.sub.2 powder is retained throughout this process, thus enabling the facile isolation of conductive colloidal-sized product particles that are suitable for direct thermal powder coating onto carrier particles. More specifically, the present invention is directed to conductive colloidal polymeric powder compositions containing therein, known conductive aromatic and heteroaromatic polymers, for example, poly(pyrrole), poly(thiophene) or poly(azulene) and their congeners, and which compositions are interstitially polymerized in the amorphous regions of fluorinated polymer resins.
Intrinsically conducting polymers or ICPs and composites of one or more ICP and a host polymer are known and have been described, reference for example, the aforementioned copending application, U.S. Ser. No. 07/176,187 (D/93298) filed Jan. 3, 1994, and references cited therein. However, applications of these materials have been limited by poor processability characteristics and low thermal and oxidative stability. Further, there is disclosed in the aforementioned copending application a composition comprised of a conductive composite comprised of an aromatic or heteroaromatic polymer comprised of monomer or monomers selected from the group consisting of pyrrole, indole, thiophene, thianaphthene, indene, azulene and ring pendant substitutent derivatives thereof; and a block or graft copolymer selected from the group consisting of ionophoric and ionomeric copolymers wherein the block or graft copolymer has at least one apolar segment and at least one ion binding segment, and processes for the preparation of said conductive composites.
Conductive magnetic brush (CMB) development systems are known in the art and provide for efficient, reliable, and cost effective xerographic development means. These systems have been prepared through powder coating by partially coating conductive carrier cores with electropositive or electronegative polymers to provide a balance of control over conductivity and tribo charging characteristics, for example, as disclosed in U.S. Pat. No. 5,015,550, issued May 14, 1991 to Creatura et al. CMB carriers have also been obtained by solution coating of mixtures of polymers and conductive particles, typically carbon black, onto various conductive and insulative carrier cores to yield developers of controlled conductivity, for example, as disclosed in U.S. Pat. No. 5,102,769, issued Apr. 7, 1992 to Creatura. Submicron polymer/carbon black composites particles prepared by suspension polymerization techniques have also proven useful in the preparation of CMB carriers by powder coating processes as disclosed in, for example, U.S. Pat. No. 5,236,629, issued Aug. 17, 1993, to Mahabadi et al. The CMB carriers obtained through partial coating provide a limited range of control over conductivity and tribo, moreover, these systems may be more humidity sensitive than fully coated carriers and may not yield tribo and conductivity stability over extended periods of time, due to impaction of toner onto the uncoated areas of the carrier core. Solution coating of polymer/conductive particle mixtures can yield the required conductivity and developer life characteristics, however, their preparation is complicated by the requirement of controlling the emission of volatile organic compounds into the environment. Suspension polymerized resin carbon black composites have provided effective, conductive electropositive materials, reference the aforementioned U.S. Pat. No. 5,236,629. However, there continues to be a need for electronegative conductive composites in the form of submicron particles suitable for powder coating.
Fluoropolymers such as the aforementioned PVF.sub.2 materials are ideal electronegative polymers but they are not readily amenable to suspension polymerization processes because of their gaseous character of the monomer and limited solubility and dispersibility characteristics of the polymer.
A preferred process for preparing carrier particles is by powder coating processes, reference for example, U.S. Pat. No. 4,937,166, issued Jun. 26, 1990, to Creatura et al., wherein, for example, a carrier composition comprised of a core with a coating thereover comprised of a mixture of first and second polymer resins that are not in close proximity thereto in the triboelectric series is described. That is, one polymer is electropositive and imparts a negative triboelectric charge to the toner, and the second polymer is electronegative and imparts a positive triboelectric charge to the toner. The resulting developer has a triboelectric value which is intermediate between the electropolarity imparted by the first and second resins.
When a carrier coating or composition with different triboelectric characteristics is desired, different batch processing conditions must be employed and may require considerable experimental trial and error to arrive at a desired coating composition and process conditions.
Environmental instability, lack of mechanical strength and integrity, and difficulties in processing have represented major barriers to commercial application of intrinsically conducting organic polymers. Among ICPs, poly(pyrroles) and poly(thiophenes) are acknowledged to be among the most environmentally stable. Their synthesis is relatively simple. Developmental activities seeking to exploit commercial applications of intrinsically conducting polymers have focused on improved processing and mechanical integrity in these materials. Poly(thiophenes)and poly(pyrroles) obtained by conventional processes are typically intractable, see for example, Advanced Materials, Volume 5, Number 9, September 1993, Part 2, page 646 to 650. Thus, there remains a need for highly conducting, environmentally stable and easily processable polymer composite materials.
There also remains a need for conductive colloidal materials, particularly negative contrast materials, that are suitable for use in known thermal powder coating processes and that can be used in preparing conductive carrier coatings.
The present invention provides melt processable, electronically conducting or semiconducting thermoplastic composites of intrinsically conducting organic polymers that are polymerized within the amorphous regions of certain fluorinated polymers. The present invention further specifies processes for the preparation of these conductive composites and provides processes for making electrically conductive carrier coatings and xerographic developers therefrom.
The composite compositions of present invention are prepared in embodiments, by in situ polymerization of aromatic and heteroaromatic monomers such as thiophene, pyrrole, indole, indene, and azulene, or a congener, for example, 3-methyl pyrrole, bithiophene, 3-alkylthiophenes, thianapththene, and the like, in the presence of at least one fluorinated polymer.
The present invention, in embodiments, overcomes the performance and processability problems associated with the ICP compositions of the prior art by forming melt processable, submicron composite particles comprised of a conducting aromatic or heteroaromatic polymer and a fluoropolymer. The conductivity of the composite can be readily controlled by variation of the ICP and/or its amount and distribution in the composite particles. The present invention provides polymeric composite compositions which are, melt processable, and exhibit specific stable and controllable levels of conductivity. The composite particles are particularly well suited for powder coating applications.